docs: def render(self, obj, opt=None):
          """ render a Schema/Parameter
  
          :param obj Schema/Parameter: the swagger spec object
          :param opt dict: render option
          :return: values that can be passed to Operation.__call__
          :rtype: depends on type of 'obj'
          """
          opt = self.default() if opt == None else opt
          if not isinstance(opt, dict):
              raise ValueError('Not a dict: {0}'.format(opt))
  
          if isinstance(obj, Parameter):
              if getattr(obj, 'in', None) == 'body':
                  return self._generate(obj.schema, opt)
              return self._generate(obj, opt=opt)
          elif isinstance(obj, Schema):
              return self._generate(obj, opt)
          else:
              raise ValueError('Not a Schema/Parameter: {0}'.format(obj))